1. Field of the Invention
This invention relates to an aspiration/infusion apparatus for body cavities, and in particular to a precision apparatus adapted for maintaining the pressure within an eye cavity during simultaneous removal and replacement of fluid therein, for example, during opthalmic surgery for removal of cataracts.
2. Description of the Prior Art
A variety of devices are known in the art for control of intra-ocular pressure. Such devices are sometimes combined with hand-held tools adapted for removal and aspiration of intra-ocular material or infusion of fluid to replace the aspirated material. The need to precisely control pressure is known, but in general, the currently available devices are complicated and expensive.
Surgical procedures for removal of cataracts now conventionally involve surgery on a normally pressurized eye. Instruments are passed through small incisions at the edges of the cornea in order to access and remove opaque cataract material clouding the lens, located immediately behind the anterior aqueous chamber of the eye. Cataracts in the lens are broken up by cutting apparatus or vibratory apparatus, and the broken-up material is aspirated together with a quantity of the aqueous fluid in the chamber. In order to maintain normal pressure within the eye, the aqueous fluid is simultaneously replaced by means of a gravity-powered infusion of a balanced salt solution supplied through a needle inserted in the anterior chamber or through a passage in the incision or aspiration instrument. Accordingly, the conventional means of pressure regulation during endophthalmic surgery is to ignore the extent of fluid flow and any variations thereof, and to employ a pressure regulation technique only. In other words, an indefinite quantity of fluid is supplied so long as intra-ocular pressure is less than a predetermined reference pressure.
A cutting apparatus having a co-axial passage for aspiration or infusion is shown in U.S. Pat. No. 4,314,560-Helfgott, et al. A handpiece is disclosed in that patent for conducting operations in the aqueous, vitreous or other intra-ocular tissues. Although both aspiration and infusion are discussed, it appears that these procedures are to be undertaken consecutively rather than concurrently. Pressure is controlled by physical elevation of a column of saline solution connected by a conduit to the intra-ocular chamber being treated.
In U.S. Pat. No. 4,184,491-McGannon and No. 4,157,718-Baehr, two hypodermic needles are inserted into the anterior aqueous chamber of the eye, one of the needles being connected to a pressure regulation device comprising an elevated column of saline solution, and the other being connected to an open tube, providing an unobstructed bleed-off pathway or drain pathway for aspirated fluid. The bleed-off pathway presumably relieves excess pressure which may develop, without the possibility of a reverse flow of fluid toward the supply of saline solution. On the other hand, the unterminated bleed pathway means that a steady current of fluid must be supplied through the pressure regulating device, the fluid flowing through the aqueous chamber of the eye and being bled away, just to maintain pressure. Without regard to whether or not cataract material is removed, the technique requires a flow of fluid through the eye.
U.S. Pat. No. 3,902,495-Weiss, et al., teaches a combined infusion and aspiration device in which an ultrasonic vibration is employed to emulsify cataract tissue. A constant flow pump withdraws emulsified lens tissue and fluid, and an elevated column supplies the fluid. As in McGannon and Baehr, the control seeks to maintain constant pressure at the input. Accordingly, the device not only incidentally causes a steady-state current through the eye, but in fact powers such a flow. According to prior art methods such as those of McGannon, Baehr and Weiss, a relatively large quantity of fluid is forced to wash through the anterior aqueous chamber. During the course of even a brief operation, completing thirty changes of the approximately one cc of fluid present in the anterior aqueous chamber is not uncommon. Special solutions which comprise balanced salt ingredients are available to most nearly satisfy the natural requirements of the eye; however, it is preferable to minimize flow of such foreign fluid, particularly flow using a powered means which is prone to malfunction, causing unnatural over-inflation or under-inflation of the eye.
In U.S. Pat. No. 3,812,855-Banko, a variety of pressure and suction configurations are selectable by the user in order to meet the requirements of a particular surgical procedure. Both a pressure source and a suction source are selectably valved by means of an electrical control mechanism. The availability of a pressure source as well as a suction source, including various sensing and controlling mechanisms, provides the machinery necessary to normalize any detected over-pressure or under-pressure situations. Such over-pressure and under-pressure problems, however, are likely to be caused by the use of powered sources and drains in the first place. The separation of the source and drain powering mechanisms presents a possibility that unwanted or dangerous pressure differentials could be produced, for example upon failure or obstruction of the source or drain. A very dependable system in which the user is relatively assured that over-pressure or under-pressure conditions could not occur is highly preferable over the most sophisticated arrangements in which a variety of malfunction-prone sensors, conduits and valves, each requiring attention, are simultaneously operative.
The maintenance of normal pressure within an eye during surgical procedures is important for a number of reasons. A constant pressure, at a natural level, tends to preserve and stabilize the spatial relationships of the intra-ocular tissues. These spacial relationships are important in order to maintain the optical parameters of the lens and eye. Variation of pressure during the operation may detract from the surgeon's ability to focus on intra-ocular tissues. Excess pressure, as known in connection with glaucoma, restricts blood circulation to eye tissues, causing damage. Nerve cells lost, for example due to oxygen starvation caused by lack of circulation, cannot be recovered. Overpressure closes off circulation through the capillaries. Variation in pressure, and also excess volume of flow through the eye, can result in loss of endothelial cells. These cells generate a natural fluid flow to the cornea, and their loss can be a cause of clouding in the long run. Another consideration is the statistical increase in probability of infection which must result from introduction of an increased volume of foreign fluid.
Conventional teachings in the art regarding pressure control have not kept pace with the sophisticated incision and emulsification apparatus known in the art. Excess flow is ignored and only pressure is controlled. Instead of instruments which are both precise and highly dependable, the art teaches pressure and flow control apparatus which although probably precise are highly complicated.
Aside from the relatively delicate apparatus and special needs of opthalmic surgery, devices are available for more or less simultaneously exchanging a body fluid with a fluid held in an external container. U.S. Pat. No. 4,112,947-Nehring teaches a combined irrigator and evacuator for closed wounds. A single housing defines a space divided into two sections by a movable divider. The divider may be spring biased or mounted on a resilient membrane which biases the device, providing pressure to empty a reservoir into the wound, and to extract a quantity of fluid from the wound. Various stopcocks, check valves and access points are provided for initially biasing the device, or for maintaining required conditions.
U.S. Pat. No. 3,411,502-Hofstra, et al., teaches sequentially infusing and aspirating small volumes of fluid, for example, to quickly accomplish a blood transfusion in newborns having Rh difficulties. Simultaneously operated expansible chambers are connected in a "Y," and valved such that one of the chambers discharges forward and draws fluid from rearward, and the other chamber operates oppositely. Both chambers have associated reservoirs and each requires at least one one-way valve. By pumping the paired chambers, an overall effect of moving fluid from a first reservoir to a body cavity, and from the cavity into a second reservoir, is accomplished. Of course, such an apparatus will result in a periodic variation in flow rate and pressure, due to the pumping of the paired expansible chambers. Therefore, the apparatus is not believed to be useful for intra-ocular manipulations.
According to the invention, intra-ocular pressure is maintained at its normal value, and aspiration of emulsified tissue may proceed, without requiring a large steady-state flow of fluid, as required in the saline column/drain apparatus. Sufficient fluid to accomplish the aspiration of cortical material and/or emulsified cataract material and the replacement of the aspirated material with an infusion is supplied; however, this is not done by depending upon an asymmetrically-powered flow through an open drain tube. Moreover, separately controlled or separately operable pressure and suction supplies are avoided. Any obstruction or disturbance in the supply or in the exhaust will not develop into an imbalance in the pressure of fluid supplied, because supply and removal of fluid are positively linked.
According to the invention, expansible supply and exhaust chambers are directly linked to one another, and the linked system is driven in a closed loop. Should any obstruction occur, for example, in the supply side, the linkage of the supply and drain mechanisms will cause both to cease operation, thereby absolutely preventing deflation, over-inflation or other pressure variation in the eye. The device may comprise piston and cylinder assemblies, such as syringes, or other expansible bodies, directly and mechanically linked. In normal operation the mechanical linkage absolutely precludes any variation between the rates of supply and discharge of fluid, which rates would otherwise require individual attention and balancing. The device can be embodied in a series of attachments, and may also be adapted for use together with an incision, aspiration and infusion tool, for example, having a series of concentric passageways.